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C-Wire Check product guide

Google Nest Learning Thermostat (4th gen) with Nest Temperature Sensor (2nd gen)

Multi-stage 24V systems run through the Google Home app, in homes with or without a C wire

Google's top thermostat, bundled with one room sensor, a trim plate and a steel plate. The maker lists up to three stages of heat and cool, three-stage heat pumps with aux and emergency heat, plus humidifier, dehumidifier and ventilation terminals. Power Sharing means no C wire in most homes, and control runs through Google Home and Matter.

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Published specifications

  • Maker: most 24V systems; heating and cooling 1-3 stages; heat pump to 3 stages with AUX, AUX2 and E
  • Maker: star connector takes only one of W3, Y3, G3, E, HUM or DEHUM; AQ+/AQ- limited to Y3 or VENT/HUM/DEHUM
  • Maker: Power Sharing works with or without a C wire; under 1% of homes may need a C wire or Nest Power Connector
  • Maker: Wi-Fi 802.11n on 2.4 GHz and 5 GHz; works with Google Home and Matter; Google Home app required to set up
  • Maker: 3.9 in diameter, 1.1 in deep, 5.7 oz; 2.7-inch 600x600 circular display; Soli, temperature, humidity, light sensors
  • Warranty: Google Store lists 2 years retail and 5 years for HVAC pros; the listing's warranty PDF says one year

Fit and limits

Strengths

  • Maker publishes the exact stages and terminals, including three-stage heat, cool and heat pump support
  • Trim plate, steel plate and a Nest Temperature Sensor are all in the box
  • Works without a C wire in over 99% of homes by Google's own figure, and takes 2.4 GHz or 5 GHz Wi-Fi

Caveats

  • Setup requires the Google Home app and account; Alexa or Apple control goes through Matter and may need a third-party hub
  • Warranty length differs between Google's spec page and the warranty PDF on the listing, and covers authorised resellers only
  • The extra terminals are shared: you cannot use W3, Y3, G3, E, HUM and DEHUM all at once

A thermostat and a room sensor, in one box

This ASIN is the bundle: the Nest Learning Thermostat (4th gen) in Polished Obsidian together with a Nest Temperature Sensor (2nd gen). Google's own box list for the bundle is the thermostat display, the thermostat base, a trim plate, a steel plate, mounting screws and wiring labels, and the temperature sensor. The trim plate covers paint marks and drywall damage left by the old thermostat; the steel plate is there for mounting onto an electrical box. Both are included, which is not true of every thermostat in this price bracket.

Google gives the display as 3.9 inches in diameter and 1.1 inches deep, weighing 5.7 ounces, and notes that the measurement is for the thermostat display only. The screen is a 2.7-inch circular LCD at 600 by 600 pixels. Amazon's specification table gives product dimensions of 0.04 by 0.15 by 0.15 inches, which is obviously not a thermostat; use Google's figures.

The sensors Google lists inside it are a Soli sensor for Motion Sense, temperature, humidity and ambient light. The Soli radar is what drives the far-sight display behaviour the listing advertises. The room sensor in the box is what lets the system read a temperature somewhere other than the hallway, and Google says the thermostat works with any Nest Temperature Sensor.

The stages Google says it can control, and the connector limits

Google's spec page is unusually specific, and it is the page to read before you buy. It says the 4th gen works with most 24V systems including gas, electric, oil, forced air, heat pump and radiant. It lists heating at one, two and three stages (W1, W2, W3); cooling at one, two and three stages (Y1, Y2, Y3); heat pump up to three stages with one or two stages of auxiliary or alternate heat plus emergency heat (O/B, AUX, AUX2, E); fan at G, G2 and G3; power at C, RH and RC; humidifier and dehumidifier (HUM, DEHUM); and ventilation (VENT). That is a wider range than most consumer thermostats claim.

There is a catch buried in the same paragraph. Google says the thermostat's star connector can accept only one of these wires: W3, Y3, G3, E, HUM or DEHUM. The AQ+ and AQ- connectors can only accept Y3, or a 1-wire or 2-wire VENT, HUM or DEHUM. So the long list of supported stages is not a list of things you can run all at once. If you want, say, three-stage heat and a whole-house humidifier and a ventilator, count your connectors first.

Google names one system type it does not cover here by simply not listing it: nothing on the spec page offers line-voltage or millivolt support, and everything is framed as 24V. Amazon's table says "Specific Uses For Product: Air Conditioner", which tells you nothing useful. The page ends every compatibility paragraph the same way, and so do we: run your own wires through Google's checker at g.co/nest/works before you buy. We are not going to give you wiring instructions here.

No C wire in most homes, but Google names the exception

The listing bullet says no C wire is required for installation in most homes. Google's spec page explains the mechanism and then qualifies it. Under Power compatibility it describes patented Power Sharing technology and says the thermostat is designed to work whether or not your home has a common wire. Then it adds that in limited cases, which it quantifies as under one percent, a C wire or a Nest Power Connector may be necessary so that the HVAC system can supply enough power in all conditions.

That means a small but real chance of a second purchase or an extra wire run. Google's checker is the tool that tells you which case you are in, and Google's own page points there specifically for the power question as well as the wiring question. The Nest Power Connector is a separate Google part, not something in this box.

The power description itself is also worth reading against Amazon's table. Google lists the power source as HVAC system wiring, with a built-in rechargeable lithium battery and consumption of less than 1 kWh a month. Amazon's table lists the power source as "Battery Powered" and says one CR2 battery is required and included. Those describe different things. Treat the maker's description as the one that governs, and expect the thermostat itself to be drawing from your system wiring.

Control runs through the Google Home app, then through Matter

Google states two requirements plainly. Installation and setup require the Google Home app, which means a Google account and a phone are part of the install, not an optional extra. And under smart home compatibility Google says it works with Google Home and Matter, and that you can control it with Google Home and other Matter-enabled apps and voice assistants.

The Amazon bullet goes further, saying you can use your voice with Alexa, Siri or a Google Assistant smart speaker. Google's own spec page does not name Alexa, Siri or Apple HomeKit anywhere; it routes third-party control through Matter, and its footnote says that to control Matter-enabled Google devices with a third-party platform or app you may need a device that works as a Matter hub from that third-party manufacturer. Amazon's table separately lists Apple HomeKit as a controller type. If Alexa or Apple Home control is the reason you are buying, confirm on your platform's own Matter documentation that you have a hub that qualifies, rather than trusting the listing bullet.

On the network side Google lists Wi-Fi 802.11n on both 2.4 GHz and 5 GHz, so either band will do. The thermostat is ENERGY STAR certified, and Google lists English, French and Spanish as the available languages.

Three different warranty periods are in play

Google's spec page for this model lists a 2-year standard warranty for retail and a 5-year standard warranty for HVAC pros. The only warranty document the listing itself supplies is the Google Consumer Hardware Limited Warranty for the USA and Canada, and that document says Google warrants a new Google product free from defects in materials and workmanship for one year from the date of original retail purchase, and 90 days for a product refurbished by Google or an authorised third party.

We are not going to guess which applies to your order. The in-box document itself says that where it differs from the online Limited Warranty at g.co/devicewarranty, the online version supersedes it, so check the current online text for this specific product before relying on any of the three numbers.

One clause matters more than the term length on a marketplace listing. The warranty document says it is only valid and enforceable where the product is sold, and applies only if you purchased from Google or its authorised resellers. It also excludes consumable parts such as batteries, damage from misuse or neglect, servicing by anyone other than Google-authorised technicians, and anomalies in the electrical current supplied to the product. Check who the seller actually is on the offer you select, and keep the receipt.

What to verify before you order

The identity fields on this listing are mixed. Amazon gives the Model Number as CE911542 and the Manufacturer Part Number as GA05169-US, and lists two UPCs, 193575038476 and 193575040189, which is what you would expect on a bundle of two products. The model name and the box contents match Google's bundle page, so the product identity is sound; just use the part number from the label on what arrives if you need it for a rebate claim.

Everything else in the Amazon specification table on this listing should be treated as unreliable: the dimensions are wrong by two orders of magnitude, the power source contradicts the maker, and "Control Type: Button Control" sits next to "Display Type: Touchscreen". None of that changes the product, but it does mean the table is not a source. The bullets and the product description are Google's own copy and line up with the Google Store page.

The two checks worth doing before you buy are the compatibility checker with your actual wires, and, if you plan to control it through Alexa or Apple Home rather than Google Home, confirming that you already own something that works as a Matter hub for that platform. The savings claim in the listing, up to 31 percent on heating and cooling, is Google's own marketing figure and depends on your house, your rates and your habits.

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Check this model on Amazon

Confirm the model, included parts and availability before ordering.

Primary sources

  1. Google Store tech specs and wiring compatibility, Nest Learning Thermostat (4th gen)
  2. Google Consumer Hardware Limited Warranty PDF supplied with the Amazon listing
  3. Google Nest compatibility checker named on the Google Store specs page and in the listing

Primary sources checked .

Compare with

Side-by-side pages, this model next to: Sensi Smart Thermostat ST55, Google Nest Thermostat (Charcoal), Mysa Smart Thermostat V2 for Electric Baseboard Heaters (BB.2.0.01.NA-US), ecobee Smart Thermostat Premium with SmartSensor, ecobee Smart Thermostat Essential (EB-STATE7-01).

Keep comparing

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